Color stabilization of glycosides

ABSTRACT

Desirable color of glycosides are obtained through bleaching and stabilization with a source of sulfur dioxide.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to glycoside materials.

2. Description of the Art Practices

It has long been known that alkyl glycosides have surfactant propertiesand are therefore desirable as either the sole surfactant, or incombination with other surfactants, in cleaning products. A glycoside asused herein means a material which contains 1 or more units of a sugarsource such as glucose and a hydrophobic organic tail. If the glycosidecontains glucose units, then it is referred to as a glucoside. If theglycoside contains 2 units of glucose, e.g. a polymer, then the materialis referred to as a glycoside having a degree of polymerization (D.P.)of 2. If the glycoside is an alkyl glycoside then the material issubstituted in the one position with an alkoxyl moiety rather than theC₁ hydroxyl of the starting sugar. Therefore, the attachment of thealkoxyl moiety is by an acetal linkage to the sugar.

It has been suggested by Boettner in U.S. Pat. No. 3,219,656 issued Nov.23, 1965 that an acid catalyzed route for obtaining an alkylpolyglycoside (APG) may be utilized starting with a saturated alcoholand dextrose. Similarly, Mansfield in U.S. Pat. No. 3,547,828 issuedDec. 15, 1970 teaches a method of obtaining glycosides.

U.S. Pat. No. 3,974,138 issued to Lew on Aug. 10, 1976 states that it ispreferable to use glucose as a starting material for the preparation ofbutyl polyglycoside. It has been observed, according to Lew, that it isextremely difficult when starting with the sugar source to obtain higheralkyl polyglycosides directly. That is, the starting sugar materials arehighly water-soluble whereas dodecyl alcohol (to add a C₁₂ group) isextremely water-insoluble. Therefore, the route proposed by Lew is toform an intermediate butyl glycoside and to thereafter transetherify toobtain the higher alkyl polyglycosides. In such a reaction, butylalcohol is generated as a by-product.

The removal of alcohols formed in transetherification is described byMao in U.S. Pat. No. 4,393,203 issued July 12, 1983. In the disclosure,Mao states that it is desirable to remove the alcohol formed because ofits adverse effect on the surfactant properties of the alkylpolyglycoside. Mao further states that the color properties of hisproduct are not adversely affected by the processing described in hispatent.

European Patent Application No. 82305283.5, published as 0077167 on Apr.20, 1983 states that various reducing agents may be utilized in theprocessing of alkyl polyglycosides. The teachings of the 0077167publication are that the reducing agent must be present with an acidcatalyst which is used to react the alcohol with an aldose or ketose.The reducing agents stated to be useful are acids such as phosphorous,hypophosphorous, sulfurous, hyposulfurous, nitrous and hyponitrousacids. It is further stated that the composition containin the reducingagent remains in the acid form.

European Patent Application No. 83200771.0 published on Dec. 28, 1983 as0096917 to Farris describes the preparation of alkyl glycosides using anacid catalyst at from 80° C. to 150° C. The 0096917 publication furtherstates that a long-chain monohydric alcohol is used to form theglycoside by continuously or incrementally adding the monosaccharide andcatalyst such that no more than 10% by weight of unreactedmonosaccharide is present at any given time and that the average amountof unreacted monosaccharide not exceed 5% by weight of the mix. Thestated reason for controlling the amount of saccharide present in thereaction mix of Farris is so that there is substantially a single phasepresent. U.S. Pat. No. 3,450,690 to Gibbons issued June 17, 1969discusses the use of alkaline materials to remove alkali sensitive colorbodies from an alkyl glucoside mixture.

European published application No. 102,558 discloses borates as beinguseful in preparing glycosides. It is further known thatN-methyl-2-pyrrolidone may be utilized as a reaction medium to obtain asubstantially single phase reaction between a saccharide and an alcoholto form an alkyl glycoside. It is also known that long-chain alkylglycosides may be formed directly from a saccharide by utilizing a smallamount of a previously prepared long-chain alkyl glycoside to render thesaccharide and the alcohol compatible.

It has been disclosed in European published application No. 0099183 ofShort (Jan. 25, 1984) that saccharides may be converted into glycosidesof up to 6 carbon atoms by forming a liquid dispersant system containingthe monohydric alcohol to be added. The liquid dispersant systemincludes acetone, ethylene glycol, methanol or ethanol and about 2 to 25moles of water per saccharide molar unit. This reaction is stated totake place at superatmospheric pressure to maintain the dispersants in aliquid state.

The art has recognized several methods of obtaining and treatingglycosides, yet color of the end product remains a problem. There has asyet not been an effective manner of maintaining a glycoside in adesirable lightly colored state. That is, alkyl glycosides as obtainedare a dark amber color and for many uses, such as cosmetics or detergentproducts, it is desirable that they have no more than a straw yellowcolor.

It has been observed herein that even in products which have beendecolorized that the color will degrade in the product upon standing.Therefore, it is desirable, and the present invention deals with,obtaining and stabilizing good color in alkyl glycosides.

Throughout the specification and claims, percentages and ratios are byweight, temperatures are degrees Celsius and pressures are inatmospheres over ambient unless otherwise indicated.

To the extent that such references are applicable, each of the foregoingis incorporated herein by reference.

SUMMARY OF THE INVENTION

This invention describes a process for bleaching organic materialsincluding glycoside surfactants comprising the steps of:

(a) obtaining a mixture of the organic material;

(b) exposing the organic material to hydrogen peroxide; and

(c) exposing the mixture of the organic material and the hydrogenperoxide to a source of sulfur dioxide; and

recovering the bleached organic material from the process.

A further aspect of the invention is a process for bleaching an organicmaterial including glycosides comprising the steps of:

(a) obtaining an aqueous solution of the organic material;

(b) exposing the organic material to a first bleaching agent; and

(c) then exposing the mixture of the organic material and the firstbleaching agent to a source of sulfur dioxide in salt form; and

recovering the bleached organic material from the process.

A third embodiment is a process for stabilizing the color of an organicmaterial including glycosides comprising the steps of:

(a) obtaining an aqueous solution of a glycoside;

(b) thereafter introducing a sufficient amount of a source of sulfurdioxide to stabilize the color of the glycoside,

thereby substantially avoiding color degradation of the glycoside.

The product described herein is a composition of matter comprising ableached glycoside and a sufficient amount of a source of sulfur dioxideto substantially inhibit color degradation of the glycoside.

DETAILED DESCRIPTION OF THE INVENTION

The present invention allows for the conventional preparation of alkylglycosides such as described in any of the references incorporatedherein. Basically, a long-chain alcohol preferably containing from 6 to22, preferably 8 to 20, carbon atoms and which is saturated is reactedonto the saccharide molecule. The addition of the long-chain alcohol maybe by way of an intermediate such as by first obtaining a methyl throughhexyl glycoside and then by transalcoholysis to obtain the long-chainalkyl glycoside. The direct route of going from the sugar to thelong-chain glycoside may also be utilized.

The term polyglycoside refers to a D.P. 2 and higher material. It isalso to be noted herein that the D.P. value is stated as an averageinsofar as a mixture of glycosides will be obtained. That is, whenstarting with polysaccharides, it would be expected that D.P. 1 throughhigher materials, e.g. D.P. 20, would be obtained. It has also beenobserved, however, that higher D.P. products will be obtained even whenusing as the sole saccharide source a material such as dextrose which isa monomer. Accordingly, the products obtained result not only fromacetal formation but also from polymerization. Similarly, some of thehigher D.P. materials may be hydrolyzed in processing to give lower D.P.glycosides. Preferably, the D.P. of the glycosides herein is from 1.0 to15, preferably 1.5 to 6 when a polyglycoside is the product. Thepreferred glycoside herein is a glucoside. The term glycoside alsoembraces derivatives of glycosides such as the alkylene oxide adducts ofMansfield (U.S. Pat. No. 3,640,998 issued Feb. 8, 1972).

The alcohol which is generated by the transalcoholysis route may beremoved or left in the reaction mixture during the initial stages. As itis desirable to have only the long-chain alkyl glycoside present for itsintended use as a surfactant, the alcohol is desirably removed. This isnot only for purposes of enhancing the surfactancy of the compositionbut the removal of alcohol also minimizes the amount of bleaching agentwhich is required.

It has been found herein that while a source of sulfur dioxide as laterdescribed might be utilized as the bleaching agent, such is notdesirable. Basically, the source of sulfur dioxide does not have therequisite strength to sufficiently bleach the dark amber mixture to thedesirable straw yellow color. Accordingly, a stronger and more effectivebleaching agent must be utilized in the present invention. Bleachingagents which may be employed herein include ozone, hydrogen peroxide,hypochlorite salts, chlorine dioxide, percarbonates, persulfates andperacetates.

The preferred bleaching agent is hydrogen peroxide as it has beendetermined that the other materials are either too harsh, economicallyprohibitive, result in salts being present, or are not sufficientlysoluble. Hydrogen peroxide by-products are oxygen and water, thereforeit is ideally suitable for bleaching. As the products herein arecommercially sold as aqueous mixtures, the presence of water is not asignificant factor.

The purpose of bleaching the products is to eliminate polyunsaturatedconjugated compounds which are formed in making the glycosides. Thesource of sulfur dioxide stabilizes the bleached product. In the absenceof bleaching, the sulfur dioxide will not result in a desirable productcolor. When both bleaching and sulfur dioxide treatment are practiced,the color is lightened and maintained in a light state. Bleaching alonewill lighten the product, however, the product will darken upon aging.Hence, color is not simply improved by the treatment of the presentinvention but is also stabilized.

The amount of hydrogen peroxide employed in the bleaching of theglycoside is expressed at 1 part of the glycoside to from about 2,000ppm to about 100,000 ppm of the hydrogen peroxide, preferably from about5,000 ppm to about 50,000 ppm. Other bleaching agents used herein aresimilarly converted on an equivalent basis of their ability to generatea free radical.

The bleaching is conducted at from about 15° C. to about 120° C.,preferably about 40° C. to about 100° C. As the preferred bleachingagent (hydrogen peroxide) is subject to evaporative losses, the reactionis preferably conducted in a closed vessel at from about 1 to about 20atmospheres pressure.

The reaction mixture subject to bleaching preferably contains on a drysolids basis from about 15% to about 75% by weight alkyl glycosides,more preferably from about 35% to about 65% by weight. The compositionalso contains from about 5% to about 85% water, preferably from about35% to about 65% by weight. The free fatty alcohol content in themixture to be bleached should be less than about 3%, preferably lessthan 1.5% by weight. In the mixture to be bleached, the D.P. range ofthe polyglycoside is generally from about 1.5 to about 15, preferablyfrom about 2 to about 8 on average. Viscosity modifiers such as ethyleneglycol, ethanol and the like may also be included.

Following the bleaching of the reaction mixture, the product is exposedto a source of sulfur dioxide. Various sources of sulfur dioxide may beutilized including sulfur dioxide gas, sodium sulfite, sodium bisulfite,sodium metabisulfite, sodium hydrosulfite, potassium sulfite, potassiumbisulfite and mixtures thereof. Sulfurous acid may be utilized, however,it is desirable that there then be a source of alkalinity within thereaction mixture so that the sulfur dioxide gas is not lost to theatmosphere.

The amount of sulfur dioxide which is utilized is at 1 part of theorganic material to be treated per 50 ppm to about 20,000 ppm of thesulfur dioxide, preferably from about 300 ppm to about 5,000 ppm. A morepreferred range for the utilization of the sulfur dioxide is 1 part ofthe organic material per about 500 ppm to about 2,500 ppm of sulfurdioxide.

As previously noted, it is desirable that the product have a slightlyalkaline character as the sulfur dioxide should substantially remain inthe mixture with the glycoside during the entire shelf-life of theproduct. Therefore, the product should be formulated such that the pH ismaintained between about 3.5 and about 11, preferably from greater thanabout 6, to about 9. Similarly, the product should contain preferably atleast about 200 ppm of sulfur dioxide per part of organic materialwithin the product, preferably about 350 ppm and most preferably about500 ppm per part glycoside. As an additional benefit, the source ofsulfur dioxide functions as an antimicrobial agent in the product.

The source of sulfur dioxide should not be added to the reaction mixtureuntil the hydrogen peroxide level is below about 5,000 ppm by weight per1 part of the organic material present. Most preferably, the sulfurdioxide is not added until the hydrogen peroxide is less than about2,000 ppm.

The reason for not adding the source of sulfur dioxide until thehydrogen peroxide is depleted is that there is a reaction between thehydrogen peroxide and the sulfur dioxide. That is, if the sulfur dioxideis added too soon, then the bleaching effect of the hydrogen peroxide isminimized and the sulfur dioxide needed to stabilize the colorproperties of the composition is depleted also.

The alkyl glycosides obtained from the present invention are useful forall manner of products in which alkyl glycosides have previously beenutilized. Specifically, products of the present invention includecosmetics, light- and heavy-duty dishwashing compositions, builtgranular detergent products, foaming compositions and industrialchemicals such as oil well drilling fluids.

The following are examples of the present invention.

EXAMPLE I

An alkyl polyglucoside is obtained wherein the alkyl portion is amixture of C₁₂ and C₁₃ linear groups. The degree of polymerization(D.P.) of the glucoside is 2.7 and is obtained as 56% solids in anaqueous solution.

The foregoing material which is a dark amber liquid is blended with 2%hydrogen peroxide on a dry solids basis at an adjusted pH of 7.5 to 8.The bleaching is continued at from 65° C. to 68° C. for a period of 20hours at which time the residual hydrogen peroxide is 0.18% by weight ofthe organic material present.

The product is tested for its transmittance at a 30% solids content at470 nanometers.

The results of the transmittance test is as shown in Table I below. Theamount of sulfur dioxide added is shown as the weight of sodiumbisulfite which is used as the source of SO₂. The test in Table I isconducted following aging of the product described above for 20 hours at95° C. The sodium bisulfite is added immediately prior to the agingtest.

                  TABLE I                                                         ______________________________________                                        % T*       % Sodium Bisulfite Added                                           ______________________________________                                        0.05       0.0                                                                39.1       0.1                                                                67.1       0.25                                                               78.2       0.50                                                               80.0       1.15                                                               ______________________________________                                         *% Transmittance                                                         

Table I shows that increased levels of sodium bisulfite result in alighter colored product.

EXAMPLE II

A glycoside is obtained and bleached as described in Example I. Theproduct is tested for its storage stability at varying levels of sulfurdioxide addition through the use of sodium bisulfite. The storagestability test is run at 50° C. at the pH shown in Table II below. Theinitial percent transmittance at 30% concentration was 89 at pH 7.0 inthe absence of any sodium bisulfite.

                  TABLE II                                                        ______________________________________                                                                              % Sodium                                pH  24 Hrs   140 Hrs  260 Hrs  920 Hrs                                                                              Bisulfite                               ______________________________________                                        7.5 90.3     61.9     48.6     20.3   0                                       7.5 82.5     74.2     76.6     67.5   1.8                                     5.5 80.4     63.8     50.4     16.5   0                                       5.5 84.8     89.4     86.7     82.2   1.8                                     ______________________________________                                    

Table II shows that color-stability of the product drops substantiallywhen no source of sulfur dioxide is present in a bleached product. The %transmittance is shown at the times indicated above.

We claim:
 1. A process for bleaching glycosides selected from the groupconsisting of mono and polyglycosides and mixtures thereof comprisingthe steps of:(a) exposing the glycoside material to hydrogen peroxide;and (b) exposing the mixture of the glycoside material and the hydrogenperoxide to a source of sulfur dioxide; andrecovering the bleachedglycoside material from the process.
 2. A process for bleachingglycosides selected from the group consisting of mono and polyglycosidesand mixtures thereof comprising the steps of:(a) exposing the glycosidematerial to a first bleaching agent; and (b) then exposing the mixtureof the glycoside material and the first bleaching agent to a source ofsulfur dioxide in salt form; andrecovering the bleached glycosidematerial from the process.
 3. A process for stabilizing the color ofglycosides comprising the steps of:(a) obtaining an aqueous solution ofa glycoside; (b) thereafter introducing a sufficient amount of a sourceof sulfur dioxide to stabilize the color of the glycoside,therebysubstantially avoiding color degradation of the glycoside.
 4. Acomposition of matter comprising a bleached glycoside and a sufficientamount of a source of sulfur dioxide to substantially inhibit colordegradation of the glycoside.
 5. The process or composition of claims 1,2, 3, or 4 wherein the source of sulfur dioxide is a member selectedfrom the group consisting of sulfur dioxide, sodium bisulfite, sodiummetabisulfite, sodium sulfite, sodium hydrosulfite, potassium sulfite,potassium bisulfite and mixtures thereof.
 6. The composition of claim 4wherein there is at least 200 ppm of sulfur dioxide per part glycoside.7. The process of claim 2 wherein the bleaching agent is hydrogenperoxide and the source of sulfur dioxide is sodium bisulfite.
 8. Theprocess of claim 1 wherein the source of sulfur dioxide is not addeduntil the hydrogen peroxide is substantially depleted.
 9. The process orcomposition of claims 1, 2, 3 or 4 wherein the D.P. of the glycoside isfrom about 1.5 to about
 15. 10. The process or composition of claims 1,2, 4, or 4 wherein the glycoside is a glucoside.
 11. The process orcomposition of claims 1, 2, 3, or 4 wherein the the glycoside is analkyl glycoside and the alkyl portion contains from 6 to 22 carbonatoms.
 12. The process or composition of claim 1 wherein the glycosideis a monoglycoside.